This invention relates to novel suspensions of solid polyisocyanates which are inactivated on the surface in isocyanate reactive compounds and to their use for various purposes.
It is already known to produce suspensions of solid polyisocyanates inactivated on their surface by adduct formation in compounds containing isocyanate reactive hydrogen atoms, in particular polyhydroxyl compounds, and to use these suspensions as heat cross-linkable, one-component systems for a wide variety of purposes (see e.g. EP-A 00 62 780, DE-OS 32 30 757 (=US-PS 4 483 974) or DE-OS 34 18 430 (=US-PS 4 619 985)). The systems known in the art often have the disadvantage of a tendency of forming blisters in the course of curing and a strong tendency of yellowing of coatings produced from such suspensions, when stored in daylight.
It has now surprisingly been found that the known suspensions can be substantially improved in these properties if the isocyanate reactive compounds forming the continuous phase comprise at least partially of polyhydroxyl compounds containing ether and ester groups, substantially corresponding to the compounds recommended in EP-A 0,209,823 (=US-PS 4,677,181) as reactants for free polyisocyanates or polyisocyanates blocked with blocking agents in the preparation of coating compounds or casting compounds. This finding is surprising since the suspensions according to the invention described below are still preferably based on aromatic polyisocyanates wherein a reduction in the tendency of yellowing in daylight was not to be expected, and in view of the fact that drying agents must be incorporated in the systems according to EP-A 0,209,823 in order to ensure satisfactory curing without the formation of blisters, as may be seen from the examples of practical application. Surprisingly, however, the use or inclusion of the ether esters of the above mentioned prior publication as continuous phase or as part of the continuous phase of suspensions of surface inactivated polyisocyanates results in a marked reduction in the tendency of blister formation in the course of curing, even without the addition of any drying agents.